Monitoring system for detecting occurrence of leakage current and/or relay short-circuit condition in an electrical system

Abstract

A monitoring system is applied to an electrical system, which includes a DC power source and an electrical apparatus that is connected to the DC power source by a pair of electric power leads incorporating respective switches. To detect leakage current from the DC power source, a low-frequency AC signal is applied via a large-capacitance capacitor to a specific connection position, between a first terminal of the DC power source and the corresponding switch, and the resultant voltage of that signal is measured. To detect a short-circuit failure of one or both of the switches, a high-frequency AC signal is applied via a low-capacitance capacitor to the specific connection position, and the resultant signal voltage is measured. Judgement as to occurrence of leakage current and/or short-circuit failure is based on the measured signal voltage values.

What is claimed is: 
     
       1. A monitoring system for application to an electrical system,
 the electrical system comprising 
 a DC power source, first and second electric power leads which connect respective first and second terminals of the DC power source to an electrical apparatus and first and second switches respectively incorporated in the first and second electric power leads; 
 the monitoring system comprising 
 a signal generating section which is controlled to generate an AC signal and is electrically coupled to a specific circuit section of the electrical system, the specific circuit section comprising the DC power source and portions of the first and second electric power leads disposed between the first and second switches and first and second terminals respectively of the DC power source, 
 a voltage measurement section electrically coupled to the specific circuit section, for measuring a voltage of the AC signal, and 
 a judgement section configured for judging, based on measurement results obtained by the voltage measurement section, whether a leakage current is flowing from the DC power source and whether at least one of the first and second switches is in a short-circuit failure condition; 
 wherein the monitoring system comprises an electrically conducting member which is at a ground potential and is insulated from the electric power leads, and comprises at least two capacitors connected between the electrically conducting member and respective ones of the first and second electric power leads, at respective positions on an opposite side of each of the first and second electric power leads from the first and second switches; 
 and wherein when the judgement section is judging whether a leakage current is flowing from the DC power source, the signal generating section generates the AC signal as a low-frequency AC signal having a relatively low frequency, while when the judgement section is judging whether at least one of the first and second switches is in a short-circuit failure condition and, the signal generating section generates the AC signal at a higher frequency than the low-frequency AC signal. 
 
     
     
       2. The monitoring system according to  claim 1 , wherein the voltage measurement section comprises a leakage current detection-use measurement section which measuries a voltage of the low-frequency AC signal and a short-circuit detection-use measurement section which measures a voltage of the high-frequency AC signal,
 and wherein the monitoring system comprises 
 a leakage current detection-use capacitor, connected between the leakage current detection-use measurement section and a specific position in the specific circuit section of the electrical apparatus, and 
 a short-circuit detection-use capacitor, connected between the short-circuit detection-use measurement section and the specific position in the specific circuit section of the electrical apparatus; 
 the leakage current detection-use capacitor having a higher capacitance value than the short-circuit detection-use capacitor. 
 
     
     
       3. The monitoring system according to  claim 2 , wherein the short-circuit detection-use capacitor is a non-polarity type of capacitor, permitting reversal of polarity of a voltage applied between terminals thereof. 
     
     
       4. The monitoring system according to  claim 2 , wherein the leakage current detection-use capacitor is an electrolytic capacitor. 
     
     
       5. The monitoring system according to  claim 2 , wherein the specific position in the specific circuit section of the electrical apparatus is predetermined as being a position at which a reversal in polarity of potential does not occur during operation of the electrical system. 
     
     
       6. The monitoring system according to  claim 5 , wherein the specific position in the specific circuit section of the electrical apparatus is at an identical potential to that of a negative terminal of the DC power source. 
     
     
       7. The monitoring system according to  claim 2 , wherein the short-circuit detection-use capacitor comprises a pair of capacitors connected in series between a positive terminal and a negative terminal of the DC power source, and wherein the short-circuit detection-use measurement section is connected to a junction point between the pair of capacitors. 
     
     
       8. The monitoring system according to  claim 1 , wherein the capacitors connected between the electrically conducting members and the first and second electric power leads are constituted by stray capacitances.